Well logging method and apparatus



J. ca. sco'r'r EIAL 2,933,144

WELL LOGGING METHOD AND APPARATUS April 19, 1960 6 Sheets-Sheet 1 FiledAug. 12, 1954 VISUAL INDICATOR MULTICHANNEL AMP RECORDER SWEEP VOLTAGEPICKUP DEVICE.

PICKUP DEVICE.

INVENTORS JAMES G- SCOTT ROLAND l4- F'ZE'EMHIV y @5555 T HOUSTON A ine,1960 Filed Aug. 12, 1954 J. G. SCOTT ET AL WELL LOGGING METHOD ANDAPPARATUS 6 Sheets-Sheet 2 ATTORNEYS April 19, 1960 J. G. SCOTT ETAL2,933,144

WELL LOGGING METHOD AND APPARATUS Filed Aug. 12, 1954 I P113- EB- 6Sheets-Sheet 5 F1E El:i

INWENTORS JAMES 6. .scorr eouwvp A. FREEMAN BY E5555 7.- Housro/vATTORNEYS J. G. SCOTT ET AL WELL LOGGING METHOD AND APPARATUS April 19,1960 6 Sheets-Sheet 4 Filed Aug. 12, 1954 PIE'I E PIIEI' E INVENTORSJHMES G. SCOTT IQOLAND A. FQEEMHN BY QEESE 7. HOUSTON HTTORNEYI April19, 1960 J. G. sco-r'r ETAL WELL LOGGING METHOD AND APPARATUS Filed Aug.12, 1954 6 Sheets-Sheet 5 MULTICH ANNEL AMPLI FIEIR R O 2 P T 6 E A, m ms m 6 m R E M S Th We RPm. T G

PHASE ADJUSTER TO A.C.6EN ERATOE.

NM r m m mrms N Nozu z Exza a w 5 w s? H? A a i 5 m #5 d B J. G. sco-r-rETAL 2,933,144

WELL LOGGING METHOD AND APPARATUS 6 Sheets-Sheet 6 April 19, 1960 FiledAug. 12, 1954 SWEEP GENERATOR TRIGGER PULSE.

TO A.C.6ENERATOZ GENERATOR- MULTlCHANNEL AMP/ PHASE ADJUSTER INVENTORS.JfiMES 6. SCOTT 20 4ND 14. FZQEEMHN BY REESE 7T HOUSTON ATTORNEVJ' WELLLOGGING METHOD AND APPARATUS Application August 12, 1954, Serial No.449,336

4 Claims. or. 181-.5)

This invention relates generally to the drilling of oil,

gas, or water or like earth wells, and more particularly pertains tomethods and apparatus for indicating and/or recording pertinentinformation during drilling operations.

In our copending application Serial No. 445,666 filed July 26, 1954, nowPatent No. 2,868,507 and entitled Well Drilling Equipment and Method,there is disclosed a drilling equipment having an electrical actuatorwhich applies impacts to a drill head at a relatively high constantfrequency. The mounting means for the drill head and the actuator mayfor example be attached to the lower end of a drill stem of rotarydrilling equipment. In operation the drill head is rotated in accordancewith conventional rotary drilling practice and the actuator is energizedto apply impacts to the drill head at a rapid rate to effect percussiondrilling. At the same time rotary mud is circulated through the drillhead for the removal of cuttings. In our additional copendingapplication Serial 452,522 filed August 27, 1954, now Patent No.2,827,263,

' and entitled Well Drilling Equipment and Method, we

have disclosed a particular embodiment of such equipment in which themotive means for rotating the drill head and the means for circulatingrotary drilling mud are built as a part of the complete assembly. Thecomplete assembly in this instance is lowered into the well by meanssuch as a cable.

The present invention is predicated upon our discovery that whendrilling operations are being carried out by our equipment, as describedabove, waves are continuously propagated from the drilling zone. Aportion of these waves are reflected and/ or refracted by thesurrounding formations. The composite wave may be detected at the top ofthe well. We have found that indications obtained from such detectedwaves reveal valuable information, including the character of theformation upon which the drill head is operating, the character of theformation surrounding the bore hole and the character of the formationbelow the drill head.

In view of the foregoing it is a general object of the present inventionto provide a novel method for obtaining valuable information duringdrilling operations, which will facilitate operation of the drillingequipment and logging of the well with respect to geological formations.

Another object of the invention is to provide a method of the abovecharacter which is particularly useful in conjunction with our welldrilling equipment previously described, which utilizes percussiondrilling by application of impacts at a constant frequency, inconjunction with rotation of the drill head.

Another object of the invention is to provide equipment suitable forcarrying out our method, including equipment for making records andvisual indications.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment has been setforth in detail in conjunction with the accompanying drawing.

Referringtothedrawings: Figure 1 is a side elevational view in sectionschemati- 2,933,144 Patented Apr. 19, 1960 cally illustrating a wellbeing drilled by the use of equipment of the type previously mentioned,in conjunction with additional equipment for the purpose of carrying outthe present method.

Figures 2A, 2B, and 2C, when taken together, form a side elevationalview in section illustrating drilling equipment of the type disclosedand claimed in our aforementioned application vSerial No. 452,522, nowPatent No. 2,827,263.

Figures 3 and 4 are cross-sectional views taken along the lines 33 and4-4 of Figures 2B and 2C respectively.

a Figure 5 is a detail in section showing the spline driving connectionto the drill head.

Figure 6 is a cross-sectional detail showing a special type of drillstem incorporating current carrying conductors.

Figure 7 is a schematic diagram of equipment employed to carry out thepresent method showing detecting devices disposed to detect wavesreaching the area adjacent the well.

Figure 8 is a schematic diagram of equipment employed to carry out thepresent method showing detecting devices disposed to detect wavesreaching the surface at different distances from the well.

Figure 1 schematically illustrates drilling equipment of the typedisclosed in our'above mentioned application Serial No. 452,522, nowPatent No. 2,827,263.

Thus the assembly designated generally at 1 is attached to the lower endof the drill stem 2. At the top of the well conventional equipment suchas a rotary table 3 is employed for rotating the stem during drilling. Aswivel head 4 is attached to the upper end of the Kelly 7 and is carriedby the traveling block 5 of a conventional drilling derrick. The swivelhead 4 is connected to a pipe 6 for introducing mud under pressure. Mudis discharged downwardly through the drill stem, through ducts in thedrill head 10, and then flows upwardly between the stem and the wellcasing or wall to the surface of the well, where it may be dischargedthrough pipe 8.

In the present instance it is assumed that the assembly l is the same asdisclosed in said copending application. Such an assembly is disclosedin Figures 2A-2C, inclusive. In general, this assembly serves to carrythe drill head 10, and it includes an electrical actuator which'isadapted to apply vertical impacts to the drill head at a constantfrequency to effect percussion drilling. Drill head 10 is disposed atthe lower end of the tubular housing 11, the latter serving to encloseand mount the assembly. The electrical actuator is designated generallyat 12, and is of the resonant type. The upper end of the housing isattached to the coupling member 13, which in turn forms the lower end ofthe rotary drilling stern.

The drilling head 10 in this instance consists generally of a body 16carrying a plurality of toothed rotary cutter assemblies 17. Suchdrilling heads are well known to those familiar with oil and gasdrilling methods, and are manufactured in different sizes and types, forvarious kinds of drilling conditions. The threaded shank 18 of the headis engaged with the mounting member 19, which, in turn, is locatedwithin the lower part of the housing 11. The lower portion 20 of member19 is slidably received in the bushing 21, which can be made of suitablematerial, such as bronze. A suitable torque transmitting connection isformed between these parts, and may consist of a plurality of splines 22formed on the member 19, and slidably engaging slots 23 formed in thebushing 21. The bushing 21 is attached by suitable means such as thescrews 24, to the ring 26, the latter being suitably secured as bywelding to the lower end of the housing 11.

sesame A suitable seal is formed between the head and the ring 26 toprevent entrance of mud or cuttings. for this purpose We have shown adiaphragm 27 of flexible material such as fabric reinforced natural orsynthetic rubber, having its inner peripheral edge clamped to a gasketring 28, and its outer margin clamped between the end piece of the ring26 and the annular washer 29. The clamping washer 29 is held in place bythe ring 31, which is internally threaded and engaged with the threadedextcrior of ring 26. The inner margin of the gasket ring 28 is tightlyclamped between the shoulder 32 on the head and the opposed end face 33of member 19.

The upper end of the member 19 is attached to the impact transmittingbar 34 which extends concentric with the axis of the housing 11. As willbe presently explained it is theupper end of this bar that receivesimpacts from the electrical actuator. i

interposed between the member 19 and the electrical actuator there is astructure including guide means for the bar 34, and a recoil spring. Asshown particularly in Figures 213 and 20 this structure consists ofconcentric tubes 36 and 37, which have their upper ends attached to amounting ring 33, and their lower ends attached to a similar member 39.These tubes are fixed to the housing 11 as by means of the weldconnection 46. The space 41 between these tubes serves to conductdrilling mud and is connected with the mud receiving space 42 in theshank 13 of the drill head. For this purpose, space 41 is showncommunicating with a plurality of pipe fittings 43, which in turn areconnected by the flexible hose sections 44 with pipe fittings 46. Thelatter fittings directly connect through the member 19 to deliver mudinto the space 42. In accordance with customary practice the cutter headis provided with ducts (not shown) which conduct the mud to the areabeing drilled,'whereby chips or cuttings are removed.

The bar 34 is slidably fitted within the bushing 47, which in turn isfitted within the end casting 48. This casting has a lower flange 49which is clamped to the flange 51 on the lower end of tube 37, bysuitable means such as the screws 53. Suitable lubricant sealing meanssuch as the resilient O-ring seals 54 and 56, can be provided at theupper and lower ends of the bushing 47. Also suitable fittings 57 can beprovided for the introduction of lubricant.

The lower end casting 48 seats an upper annular body 53, and the latteris bored and fitted with the bushing 59. The upper end of body 58 isprovided with a flange 61 that overlies the ring 38.

The members 4-3 and 59 provide space for accommodating the loaded recoilspring 62. One end of this spring seats upon member 43, and the upperend seats upon the collar 63, which is loosely fitted about the bar 34.Coliar 63 normally engages the annular shoulder 64 on the upper end ofbushing 59 to resist the normal loading of the spring. Immediately abovethe collar 63 the rod 34 has an enlarged annular portion 66 to form theabutment shoulders 67 and 68. When no loading is being applied to thedrill head, shoulder 67 is urged against the opposed face of the collar63, by the force of the loaded spring 62.

The upper part 69 of the rod 34 forms what can be referred to as ananvil portion. It is slidably fitted within a bushing71 that is carriedby the sleeve 72. The sleeve 72 is assembled within a bore 73 formed inthe upper part of member 58, and is provided with a flange 74 adapted toseat upon the cooperating shoulder face '76. The flange 74 is urgedagainst the shoulder face 76 by suitable means such as a Bellevillewasher 77. A suitable arrangement of ducts 78 and 79 can be provided forintroducing lubricant to the area between the bushing 71 and the anvilportion 69.

The electrical actuator is preferably constructed as follows: It employsa field comprising two electromagnet assemblies-12a and 12b,-which serveto operatea central piston-like core 81. The assemblies 12a and 12b caneach consist of laminated cores 82 disposed radially about the axis ofthe central core, and provided with windings 83. The pole pieces 84 and86 of each laminated core terminate at the boundary of a cylindricalpassage 87, within which the central core 81 operates. The two sets oflaminated cores are shown separated by the mounting plate 88, and havetheir outer portions set interposed between the channels 89. Thepassages 91 formed by these channels permit passage of mud. Thisarrangement brings the drilling mud into heat exchange relation with themagnetic cores and windings, thus providing for dissipation of heat. Thelower ends of channels 39 are sealed with respect to ring 38, andpassages 91 have their lower ends in free communication with the passage41 between the tubes 36 and 37. Filler rings 92 and 93 are interposedbetween the pole pieces 84 and 86 of each electromagnet assembly, andthe filler ring 93 is interposed between the two sets of pole pieces 86.

The central pistonlil e core 81 is provided with lower and upper axialextensions 94 and 95 of reduced diameter which form impact or hammerelements. The hammer element 94 delivers impacts to the anvil portion 69or" the bar 34. A bearing assembly for element 95 can consist or" asleeve 96 which is mounted upon the laminated cores for the upperelectromagnet assembly, and which serves to mount the bushing 97. Thisbushing is bored to receive the element 95, and is also provided withsuitable means such as ducts 98, for introducing lubricant. A similarbearing assembly is formed for the lower element 94. It consists of asleeve 99 (corresponding to sleeve 96) serving to mount the bushing 101(corresponding to bushing 97). Here again the bushing can be providedwith lubricant receiving ducts 162. At its lower end face the bushing101 is in direct engagement with the upper end face of the sleeve 72.Also the lubricant ducts 102 can be in communication with ducts 78.

Overlying the upper electromagnet assembly 12a there is an annular plate196 that is fitted within the channels 89. Above this plate there is asecond recoil spring 107 and mounting means for the same. The lower endof spring 197 seats upon the impact receiving member 1%, which'has itsend face 109 aligned with and opposed to the end face of the impactelement 95. The member 108 is guided by the bushing ring 111 which isfitted in the upper portion of the sleeve 96. The upper end of thespring 107 seats upon a member 112, which ismaintained in spacedrelationship with the plate 106 by the tubular shroud 113 and theinterposed plate 13.4. The inner margin of the plate 114 forms anabutment shoulder 115 for the thrust receiving member 1&8.

As will be presently explained the windings of the electromagnetassemblies are energized by current pulsations whereby the centralcore'81 is caused to reciprocate a predetermined number of completestrokes per minute.

The weight of the moving parts, the strength and pro-loading of therecoil springs, and the frequency of excitation of the windings is suchthat the core reciprocat'es at a constant frequency. When no downwardforce is being applied to the drill head, the force of the downwardstroke of the core is absorbed by the lower recoil spring 62. However asthe load is applied to the head an increasing amount of the impactenergy is transmitted through the bar 34 to the head and to theformation, until a maximum optimum loading is reached, which is equal tothe force of the loaded spring 62. By way of example this may be of theorder of 30,600 pounds.

A suitable circuit arrangement for exciting the windings ofthevelectromagnet assemblies is shown in Figure 7. The lines L1 and L2are connected to a suitable source of alternating current, such as voltsat 30 cycles. The windings 83 have a common point of connection whichconnects with one line L1. The other. terminals of the windings 83connect with the rectifiers 116, which have a commonpoint of connectionto the other line L2. With this arrangement rectifying pulses aresupplied alternately to the two sets of windings, whereby for a currentfrequency of 30 cycles per second,

the central core 81 is reciprocated at a frequency of lower closure 119for the housing 118 can be providedwith a sealed fitting 121 toaccommodate the conducting wires leading to the windings of theelectromagnet assemblies. Also the end member 119 has a rigid sealedconnection with the member 112. Thus member 112 has an upwardlyextending cylindrical portion 122, which has a threaded engagement 123with a depending cylindrical portion 124 of the end closure 119.Suitable means such as the O-ring seals 126 provide a fluid tight sealbetween these parts. The upper ends of channels 89 are attached to thelower edge of a tubular section 127 that surrounds the tubular portion122, and which abuts the lower end face of the tubular portion 124. Alsoa ported seating ring 128 can be provided about the tubular section 127,and against which this section may seat. I

To maintain the parts of the electrical actuator in assembled relation,we have shown a plurality of tie bolts 129, which at one end engage themember 113, and at the other end engage the member 58.

By reference to Figure 2A it will be seen that the annular passage 91for circulating mud continues upwardly past the closed housing 118, tothe space 131 which overlies the upper end 132 of the housing 118. Space131 communicates with the lower end of the passage through the drillstem.

Referring back to Figure 1 it will be evident that with the assemblyillustrated at Figures 2A-2C attached to the lower end of the drillstern, it is caused to rotate together with rotation of the drill stem,and when the actuator is energized, impacts are applied to the drillhead in conjunction with rotation and the discharge of rotary mud forthe removal of cuttings.

Suitable means can be employed for extending current carrying conductorsdown into the well. For example, a suitable two-conductor cable can bethreaded through the drill stem, and at the top of the well this cablecan connect through slip rings with an exterior generator.

In place of a cable extending down into the well we prefer to use thespecial drill stem construction shown in Figure 6. Thus the sections 136of the drill stem are provided with inner tubular conductors 137 and 138made of suitable materials such as copper or aluminum. These conductorsare insulated from the drill stem and from each other by the insulation139 and 141. The inner wall of 139 can be provided with an abrasionresistant layer of insulation 142, such as a suitable synthetic rubber.The conductor tubes and the associated insulation terminate within themale and female parts 140 and 143 of the stem couplers where they formfiat end faces adapted to be compressed together to make good electricalconnection. At the top of the drill stem and in conjunction with theswivel head 4, a suitable slip ring device 144 can be provided wherebythe conductors make continuous connection with conductors of astationary cable 145. This cable is shown connected to the generator G,through the suitable control panel 146. The generator can be driven by asuitable motive device, such as electric motor or internal combustionengine.

In practice the equipment described above operates as follows: The drillstem is rotated in accordance with conventional practice, as for exampleat rotative speeds which may vary from to 350 r.p.m. and at the sametime the electrical actuator is energized by current from the generatorG, to apply impacts to the drill head at a relatively high and constantfrequency, as for example the frequency of 1,800 impacts per minutepreviously mentioned. The loading upon the drill head, that is, theforce with which the head is permitted to bear upon the bottomformation, is adjusted so that it is comparable to the loading requiredfor maximum energy transfer. In the previously mentioned example, thiswas assumed to be about 30,000 pounds.

When operated in the manner described above, the drilling equipment hasa number of remarkable characteristics which can be briefly summarizedas follows: Assuming for example that the drill head is operated upon arelatively hard rock formation, the rate of drilling with the actuatorin operation is many times the rate for the same rig operating under thesame conditions but without operation of the actuator. By way ofexample, where the drilling rate in a rock formation is of the order of1 inch per hour, with the actuator in operation the drilling rate is ofthe order of 10 feet or more per hour; This increase in drilling speedis obtained without excessive power consumption. Actually it. appearsthat the torque required for turning the drill stem is somewhat lesswhen the actuator is in operation, which is attributed to the freeingeffect of the vibrations upon all of the rotating parts. Also, this isattributed to the fact that instead of the drilling being due primarilyto the turning of the head against the formation, it is due in thisinstance to the rapid and continued impacts upon the formation, withturning of the head serving primarily to distribute the impact pattern.

When using the drilling equipment described above, it is desirable andimportant to secure information pertinent to the geological formationsencountered as well as the formation immediately underlying andsurrounding the drilled area. As previously mentioned, we havediscovered that in the operation of such a head, the rapid impactsapplied to the formation in the rilling zone cause vibrations which arepropagated, reflected and/or refracted to the surface of the earth, andwhich when picked up at the surface of the earth have characteristicwave patterns. Certain characteristics of the waves as they reach thesurface of the well are modified in accordance with certain varyingconditions, and such modification when indicated by suitable apparatus,serve to impart valuable information. 1

Referring to Figure l, we have shown a number 0 pickup devices T of theGeophone type located at the surface of the earth, and distributed aboutthe top of the well. These Geophones can be transducers of the dynamictype, capable of translating shock or'sound waves into correspondingelectrical current variations. Suitable holes can be drilled forreceiving the Geophones, for each Geophone can be mounted on a bardriven into the ground. An additional Geophone (not shown) can beattached directly to the Kelly extended through the rotary tables, andhas its terminals connected to an exterior cable 147.

As suitable means for translating the current variations from thedilferent Geophones, all of these devices are shown connected to theinput terminals of the multichannel amplifier network 148, the output ofwhich is shown connected to the recorder 149, which may be one of themulti-channel magnetic tape type, and to a visual indicator 151, whichcan be one of the oscilloscope type with a separate oscilloscope tubefor each Geophone. The sweep voltage for the oscilloscope tubes can besupplied from sweep voltage generator 152 which in turn may besynchronized by a synchronizing connection with the circuit of thegenerator G.

The system described above with reference to Figure l is illustrated inbetter detail in Figure 7. The Geophone transducers in thisinstance arenumbered T1 to T9,

inclusive, with T1 to T8 being disposed symmetrically about the top ofthe well, that is, at equal radial distances from the Well, and spacedequally circumferentially. The various Geophone transducers are againshown connected to the various channels of the amplifier network 148,separate outputs ofwhich are applied to the visual indicator 151. device151 represent oscilloscope screens. The screens can be provided withvertical and horizontal base and cross hatch lines to facilitatechecking the wave patterns with respect to amplitude, shape, andrelative positioning with respect to the vertical and horizontal baselines. Voltages from the outputs of the multi-channel amplifier areapplied to the vertical deflecting electrodes of the oscilloscope tubes.A horizontal deflecting voltage of sawtooth wave form is applied to thehorizontal defiecting electrodes of the tubes, from the sweep frequencygenerating means. In Figure 7 the sweep frequency generating means hasbeen shown including a transformer E56 for deriving analternatingvoltage from the line L1--L2, leading from the generator G, togetherwith a phase adjuster 157. The output of the phase adjuster is appliedthrough the half-wave rectifier 158 to the trigger pulse generator 161,to provide sharp triggering pulses. Thesepulses are applied to the sweepgenerator 162, suitable for generating a sweep voltage having a sawtoothwave form, with each wave being of suflicient length to supply a sweepperiod which is preferably at least equal to the time period betweensuccessive strokes of the electrical actuator. Adjustment of thevariations in the phase adjuster 157 makes it possible for an operatorto change the phase relationship between the actual reproduced waveforms, and the actual impacts applied by the electrical actuator.

Assuming now that the drilling equipment is in operation at the bottomof the well, and that the well is of substantial depth, the operator cancontinually observe the wave patterns on the oscilloscope screens, andvarious characteristics of the reproduced patterns can he used to impartvaluable information. For example, assuming that the drill is proceedingthrough a relatively soft formation, the wave patterns will have acharacteristic shape and amplitude determined by such factors as theactual stroke of the drill head under the impact imparted to it, thedensity, elasticity and continuity of the formation through which thedrill is passing, and the ability of this formation and other overlyingformations to transmit sound vibrations. Assuming now that the drillengages a considerably harder formation, such as hard rock, certaincharacteristic changes in the reproduced wave form occur. The waves havemore abrupt Wave front, and the amplitude increases. Similarly,characteristic changes occur when the drill passes from a hard to asofter formation. If the drill should pass from a softer to a harder butfaulted forrnation, the axis of the maximum directivity is no longervertical, and as a result there Will be a variation in the amplitude orcomplete disruption of the wave patterns for the oscilloscopes connectedto certain of the Geophones Tl-TS. The differences in amplitude whenexamined by the operator will reveal the general direction or strike ofthe declination, and to some extent, the angle or dip of the formation.

In addition to the information referred to above, the indications of theOscilloscopes also give some information with respect to the formationsintervening between the earths surface and the bottom of the well. Thuswith the depth of the well being known, there is a phase differencebetween the wave form as received by Geophone T9 and the Waves from theGeophones which the depth of the well. Therefore, these phase differ-The circles indicated for ences when compared are an indication of thegeneral or average density, elasticity and absorptivity of theformations through which the drill has passed, and provide a continuouslog in relation to the type of formations drilled.

In addition to the information referred to above, which concerns thecharacter of the formation being operated upon by the drillingequipment, one or more Geophones and indicating devices used in themanner described above can be used advantageously to keep continuouscheck of the operation of the drill to make certain that it isfunctioning properly, and is applying percussion impacts of properintensity to the drill head. For this purpose it is sufflcient to useone Geophone together with a single indicating device, with a Geophoneeither in contact with the earth, or mounted in direct soundtransmitting contact with the drill stem.

Instead of mounting a Geophone at the top of the well on the Kelly, aspreviously described, a Geophone may be mounted upon the assembly 1,immediately above the drill head. Such an arrangement requires circuitconnections eXtcnded down into the well for making connection with thevisual indicator. Instead of using separate conductors with such aGeophone, the current variations which it produces can be imposed upon acircuit which makes use of one of the conductors for the actuator as oneside of its circuit, and the drill stem itself for the other side. InFigure 2C such a Geophone T10 has been mounted upon the housing 11,immediately above the drill head 10. Its operating element or diaphragmis in contact with the drilling mud about the housing 11.

An additional Geophone may be employed advantageously to keep acontinuous check on the consistency of the mud flowing in the drilledhole. The Geophone may be mounted, for example, near the mud dischargepipe 8 with its operating element or diaphragm in contact with the mud.The wave pattern would provide a continuous check of the consistency ofthe mud.

Another embodiment of the system described with reference to Figure l isillustrated in detail in Figure 8. The Geophone transducers in thisinstance are numbered T11 to T23, inclusive, and are radially disposedabout the well. The various Geophone transducers are again shownconnected to the various channels of the amplifier network 148a,separate outputs of which are connected to the visual indicator 151a,the operation of which has been described. The sweep frequencygenerating means has also been described with reference to Figure 7.

Assuming now that the well drilling equipment is in operation at thebottom of a well, and the well is of substantial depth, the operator cancontinuously observe the wave patterns on the oscilloscope screens. Thecharacteristics of the patterns impart valuable information respectingthe extent and depth of the formation.

Previous reference has been made to the fact that the recorder 149 canbe of the multi-channel magnetic tape type. The tape of this recordercan be operated at a suitable constant speed whereby it records all ofthe current variations from the various Geophone transducers. At a latertime such magnetic records can be used to operate visual indicators, orthe records mixed for the purpose of reproducing composite wavepatterns. Also, if desired, the records can be reproduced for thepurpose of operating a recorder of the pen type.

We claim:

1. In a method applicable to a rotary drilling rig in which a rotarydrill stem extends into the earth and carries a drilling head at itslower end, the method comprising applying vertical impacts to thedrilling head as it is being rotated against the formation, said impactsbeing applied at a constant frequency whereby periodic waves arecreated, detecting the resulting waves at the surface of the earth,forming a signal which has a predetermined phase relationship withrespect to the applied impacts, and varying the phase of saidsignal tothereby obtain a predetermined phase relationship between the detectedwaves and said signal to facilitate comparison of the phase relationshipbetween the signal and the detected waves.

2. An apparatus for logging earth wells during drilling of the samewhere the drilling operation is carried out by a rotary drilling headwhich is rapidly impacted at a constant frequency against the bottom ofthe well while it is being rotated, said apparatus comprising aplurality of wave pickup transducers located at the surface of the earthand in vibration receiving contact therewith, electrical response meansconnected to receive the output of said transducers and formingelectrical signals corresponding to the received waves, means forming asignal which has a predetermined phase relationship with respect to theapplied impacts, a phase adjuster connected to receive said last signaland serving to vary its phase with respect to the electrical signalsformed by the transducers, and means for indicating all of saidelectrical signals.

means permitting the adjustment of the phase relationship between thesignals applied to the horizontal and vertical deflection means tothereby permit rapid analysis of the signals.

4. An apparatus for logging earth wells during drilling of the same,wherein the drilling operation is carried 3. An apparatus for loggingearth wells during drilling of the same where the drilling operation iscarired out by a rotary drilling head which is rapidly impacted at aconstant frequency against the bottom of the well while it is beingrotated comprising aplurality of wave pickup transducers located at thesurface of the earth'and in vibration receiving contact therewith, eachof said wave pickup transducers serving to form an electrical signalcorresponding to the vibrations picked up by the same, amplifier meansconnected to receive each of said transducer electrical signals andamplify the same, a plurality of cathode ray means having vertical andhorizontal deflection means each connected to receive an amplifiedtransducer signal, said signals being applied to the vertical deflectionmeans of their respective cathode ray means, means forming a referencesignal which has a predetermined phase relationship with respect to theapplied impacts, phase adjusting means serving to receive said referencesignal and to vary its phase, sweep voltage generator meansconnectedtoreceive the output of said phase adjusting means, the outputof said generator being connected to the horizontal deflection means ofeach of thecathode ray means, said phase adjusting out by a rotarydrilling head which is rapidly impacted at a constant frequency againstthe bottom of the well by an electromagnetic assembly while it is beingrotated, the electromagnetic assembly being energized by an alternatingcurrent source at the surface of the well, comprising a plurality ofseismic wave pickup transducers located at the surface of the earth andin vibration receiving contact therewith, electrical response meansconnected to receive the output of said transducers and form anelectrical signal corresponding to the received seismic wave, meansforming a reference signal from the alternating current, said signalhaving a predetermined phase relationship with respect to the appliedimpacts, a phase adjusted connected to receive said refernece signal andserving to vary its phase with respect to the electrical signals formedby the transducers, a plurality of cathode ray means having horizontaland vertical deflection means for displaying said signals, one for eachof said transducers, said reference signals being applied to one of thedeflection means of each of said cathode ray means, and the electricalsignals formed by the transducers applied to the other deflection meansof individual ones of said cathode ray means.

References Cited in the file of this patent UNITED STATES PATENTS BrantDec. 27,

